1. Field of the Invention
This invention relates generally to parameter setting means for analog circuits, and more particularly to a parameter setting means which includes error correction for setting one or more analog circuit parameters.
2. Description of the Related Art
Memory devices are increasingly used in analog circuits to configure their behavior. Such circuits have associated parameters, and are arranged such that one or more of their parameters can be set via the application of a digital input word, the bits of which are stored in the memory device. Examples include setting the gain and/or offset of an amplifier, setting the cut-off frequency of a filter, calibrating an analog-to-digital converter (ADC) or digital-to-analog converter (DAC), defining an input-to-output characteristic for non-linear amplification, and defining the temperature behavior for temperature dependent gain.
In such systems, the memory device is a potential source of error. If a floating-gate memory (such as an EEPROM) is used, charge can leak away from a floating gate, eventually causing the stored data to be corrupted. If fuses are used for the memory, high electric fields across small gaps could cause material transport, eventually causing blown fuses to be detected as unblown. If latches, registers or RAM cells are used, radiation could cause the memory cell state to flip. In all of these cases, the parameter established by the stored data would change, causing the analog circuit to function differently than it would if there were no errors.
FIG. 1 shows an example of a circuit in which the gain of an amplifier 10 is set via the application of four data bits to amplifier gain inputs G[3], G[2], G[1] and G[0] (abbreviated herein as G[3:0]). The data bits are provided by a memory device 12, the outputs of which (D[3:0]) are connected to gain inputs G[3:0]. If one or more bits of the memory are corrupted, the resulting gain will be different from that programmed. This memory corruption is not detectable, so no warning can be given if the gain setting is changed from the programmed value.